0 L0 0:a61bcb200:20000 20000L/20000P F=1 B=2110309/2110309
20000 L0 0:a61b87a00:20000 20000L/20000P F=1 B=2110304/2110304
During this quick test I did not manage to craft a test which
would inflate a file in the middle without touching its other
blocks (other than using a text editor which saves the whole
file - so that is irrelevant), in order to see if ZFS can
"insert" smaller blocks in the middle of an existing file,
and whether it would reallocate other blocks to fit the set
recordsizes.
For generic filesystem uses (append, replace 1:1) at least
Bob's assessment is right - zfs stores recordsized blocks
and one possibly smaller tail block, not a series of random
sized blocks as I implied.
I might imagine situations like heavily congested systems
where zfs might cut corners to get dirty bytes out to disk
faster - and not read-merge-write tail blocks, but even if
this is implemented at all, it should be a rare condition.
//Jim Klimov
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